The coolant temperature sensor in the 2002 Ford Focus sends a signal to the computer which tells the computer how hot the coolant is in the engine. The computer uses this information to make adjustments to the timing and the fuel for optimum engine performance. The 2002 Focus has three different engines, and the ECT is located in different places on all three engines. In the 1.8-litre engine, it is located on the cylinder head. In the 1.9-litre engine, it is located on the heater hose inlet pipe. It is located at the left rear of the engine on the 2.0-litre engine.
Open the bonnet and locate the coolant temperature sensor on your particular engine.
Unplug the wiring harness connector by prying the tangs on the side of the sensor away from the plug and pulling the plug out of the sensor.
Use the appropriate size wrench to unscrew the sensor from the block, head or inlet pipe.
Coat the threads of the new sensor with anti-seize compound. Take care not to get any on the smooth sensing bulb. Screw the sensor into the block and tighten it firmly. Plug in the wiring harness connector.